function [pre_time, pre_cmd_a1, pre_fb_a1,pre_Err_a1] = pre_filter(time, cmd_a, fb_a, BiasUnit)

n = length(time);
pre_time = time(1:n-BiasUnit+1,1);
pre_cmd_a1 = cmd_a(1:n-BiasUnit+1,1);
pre_fb_a1 = fb_a(BiasUnit:n,1);

pre_Err_a1 =  pre_cmd_a1 - pre_fb_a1;